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Thread: Soundcraftsmen purchase help

  1. #211
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    A100

    Hello,
    Does any one has the schematics for the A100 model please?

    Thank you.

  2. #212
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    Quote Originally Posted by blazer40 View Post
    Try disconnecting the two main capacitors and see if either one of them is shorted also. The SCR's are common 4010's, although you can replace them with 4020 or 4025's for higher current capacity. If 1 or more SCR's are shorted you'll want to check the two drive transistors for the SCR's and also each SCR gate has a low value resistor on it, those can go open or really high when the SCR's shorts.

    -Matt
    thanks Matt, I have a decent Craftsmen DMM but it does have capacitance, how do I check the main capacitors for shorting/shorted?

  3. #213
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    A400 with only high fan speed when turned on?

    Quote Originally Posted by blazer40 View Post
    I attached a couple to get you started.

    The biggest thing to watch for is the large 10W resistor on the power supply board, make sure it hasn't desoldered itsself and that the fan spins on low when the unit is turned on.
    Matt - could be a silly and/or obvious answer here but I'm a relative newbie so I'm going to ask...

    If that large 10W resistor did become unsoldered, would the fan only just spin on high (very high in fact) when the amp is turned on? Because that's what's happening on an A400 I have.

    Thanks?

  4. #214
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    Unfortunately no, when these big ballast resistors become unsoldered the fans stop and *ONLY* spin when the protection circuits kick in. I almost always put 15 or 20 watt units in (they are usually bigger and can expel heat better) to keep board temps down. I would say this is the biggest failure point with the mosfet amps with fans. I have repaired a bunch of these units and have seen some pretty interesting *fixes* that people have devised when the fans stop running on low.


    Quote Originally Posted by Goggle1824 View Post
    Matt - could be a silly and/or obvious answer here but I'm a relative newbie so I'm going to ask...

    If that large 10W resistor did become unsoldered, would the fan only just spin on high (very high in fact) when the amp is turned on? Because that's what's happening on an A400 I have.

    Thanks?

  5. #215
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    Just use a dmm in resistance mode and put the probes across the terminals, you'll see the shorted ones immediately.


    Quote Originally Posted by Goggle1824 View Post
    thanks Matt, I have a decent Craftsmen DMM but it does have capacitance, how do I check the main capacitors for shorting/shorted?

  6. #216
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    The primary caps appear to test fine, I tested with a Blue ESR meter, both caps tested within range.

    Thinking I should check rail voltages next in chasing down this fan that runs only on high.

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